Personal samplers for the monitoring of industrial air environments sample air at the lowest possible flow rates in order to keep the instrument weight at a minimum. The efficiency of drawing airbone particulates to the sampler's inlet face and of transporting the particles from the inlet face through the inlet configuration to the particle collection medium is dependent on the volumetric air flow rate, inlet geometry, particle size and particle adhesion to the inside walls of the sampler. Except for some respirable dust standards, most present federal standards require that particles of all sizes be sampled by means of an open-face filter holder or by a closed-face filter holder with a small inlet hole. In the proposed work, the presently regulated inlet designs will be tested for their sampling efficiency as a function of particle size, particle adhesion, ambient air velocity and sampler's orientation relative to the ambient air flow direction. The sampler inlets will be tested in a wind tunnel. The overall sampling efficiency of the open-face filter holder will be determined by sampling fluorescent-dye tagged aerosols. The overall sampling efficiency of the inlet holes will be determined by sampling aerosols through the inlet into an optical single particle counter sensor. The sampling efficiency up to the inlet face will be distinguished from the losses in the inlet through the difference in performance of liquid versus bouncy, solid particles. By means of another new technique, utilizing hypodermic needle feeding of aerosols, particles will be placed into specific locations of the flow field surrounding the inlet, and the sampling efficiency will be derived from the individual particle trajectories relative to the inlet. The latter technique, in particular, is expected to result in a better understanding of inlet performances and may provide a basis for improved inlet designs suitable for future standard setting.